1. Field of the Invention
This invention relates to improvements in removable core cylinder locks and particularly to a removable core cylinder lock utilizing twisting tumblers operable by keys having at least some skew cut bits.
2. Prior Art
Removable core cylinder locks are known in the prior art as has existed for about half a century. See for example the patents to Falk, U.S. Pat. No. 1,832,108 (1931); Voight, U.S. Pat. No. 1,964,787 (1934); Falk, U.S. Pat. No. 2,061,456 (1936); Ledin, U.S. Pat. No. 2,268,511 (1941); Johnstone, U.S. Pat. No. 2,379,862 (1945); Check, U.S. Pat. No. 3,009,349 (1961); Best, U.S. Pat. No. 3,206,958 (1965); Oliver et al, U.S. Pat. No. 3,713,311 (1973); and others in this art.
Typically, a removable core cylinder lock is removable from a lock housing under the control of a control key for removing and e.g., replacing, the core. An operating key is used to operate the lock in its normal condition and does not affect the removability of the core. Some of the prior art use a special configured key for the control key, but all of the relevant prior art utilizes conventional pin tumblers and are therefore subject to picking, thus limiting the amount of security they afford. That is, they are pickable to the same extent that pin tumblers locks of their configuration are pickable. Conventional tumbler locks are also more subject to security violations with unauthorized duplicated control keys. Further, much of the prior art removable core cylinder locks are of complex construction and difficult to assemble.
Twisting tumbler locks utilizing a side bar or latch bar are known and are sold commercially by Medeco Security Locks, Inc. of Salem, Virginia and are made under the Oliver et al patent, RE 30,198 a reissue of U.S. Pat. No. 3,499,302 (1970). However, insofar as is known twisting tumbler locks have never been utilized in removable core cylinder locks because of the difficulty imposed by the configuration and the position of the latch bar.